“This is exciting,” said Darryl Jenkins, an aviation analyst. “Any time Southwest comes into your community, it’s a big deal — they have an incredible amount of consumer satisfaction.”

Southwest initially will operate 12 daily nonstop flights from Dulles: seven flights to Chicago Midway International Airport, two each to Tampa and Orlando in Florida, and one to Las Vegas. It also will offer direct or connecting service to 35 other destinations.

The airline will occupy two gates at Dulles and employ about 40 local people, it said.

The addition of Southwest at Dulles will have an immediate and positive effect on the local economy, aviation analysts said.

“I think they’ll do extremely well, and I think they’ll grow here,” said Leo Schefer, president of the Washington Airports Task Force, a nonprofit group that promotes the expansion and enhancement of Dulles and Ronald Reagan Washington National Airport.

Southwest’s low fares will attract large numbers of leisure travelers to the area, in addition to business travelers, he said.

Southwest will fill a void left at Dulles after the demise in January of budget carrier Independence Air, which at its peak operated 600 daily flights from the airport.

“And knowing that there’s a large population in Northern Virginia — one of the fastest-growing areas in the nation — we wanted to capture some of that passenger traffic,” Southwest spokeswoman Whitney Eichinger said.

With the addition of its Dulles service, Southwest now operates more than 3,100 daily flights to airports in 32 states.

Since Independence stopped service, several airlines have expanded service, including Southwest budget-carrier rival JetBlue. Two airlines have started service at Dulles in recent months: Maxjet Airways, a luxury all-business-class airline offering four flights per week to London; and Sun Country Airlines, a low-cost carrier with one daily round-trip, except on Saturdays, to Minneapolis.

But neither Maxjet nor Sun Country has the potential for growth or name recognition of Southwest.

One of the industry’s most financially successful airlines, it has maintained its success through a consistent management team and controlled growth, Mr. Jenkins said.

“They’re in no hurry — they’ll go into one or two cities a year, and that’s pretty much it, so at that rate you never outgrow your capital base. They’re very, very patient.”

Southwest’s presence at Dulles won’t diminish its role at BWI, the airline’s fourth-busiest airport, airline officials said. The airline, which began service at the Maryland airport in 1993 with eight daily flights, recently added daily flights from BWI for a total of 173. It also opened a new terminal there last year.

“Dulles will complement Baltimore,” Ms. Eichinger said.

Analysts agreed that adding Southwest service to Dulles won’t hurt BWI because the two airports rely on different communities for much of their business.

“Southwest will continue to grow at Dulles, and I don’t think that it will in any way, shape or form take away from BWI,” Mr. Shefer said.